1. Field of the Invention
The present invention generally relates to an image forming apparatus, and more particularly, to a copying apparatus provided with a plurality of toner developing devices including a white toner developing one.
2. Description of the Prior Art
A copying apparatus which is provided with a plurality of toner developing devices and capable of copying not only in black but also in other colors, for example, red and blue is now in practical use. As to copy papers, although white papers are generally used, colored ones are occasionally employed.
Conventionally, in reproducing an original, white portions thereof are generally substituted by the ground color of a copy paper and, no particular image formation is carried out with respect to these portions.
In the above described prior art, when white papers are used as the copy papers, the white portions of the original can be readily reproduced because the ground color of each copy paper is white. However, when colored copy papers are used, the white portions of the original are inconveniently reproduced by the ground color of each colored copy paper.
For example, when white portions of a photograph is desired to be reproduced in white, these portions can not be substituted by the ground color of the colored copy paper. In contrast, when a white original document having thereon printed letters is reproduced, it is not necessary to reproduce the white portions of the original document in white. If these portions are thoughtlessly reproduced using white toner, not only the white toner is unnecessarily consumed but copying process is doubled, resulting disadvantageously in prolonged copying time.